| Persimmons are important agricultural products in China,with the annual output ranking first in the world.So far,the technics of persimmon processing are still relatively backward,and processing capacity is low.Due to the fact that the market price is cheap,and farmers are unintentionally picking,many persimmons went to waste.Mat Black(MB)have corresponding health care effects,and the nutrition and function of MB are better than that of non-MB.The Mopan persimmons were used as raw material in this project,inoculated edible microbes into mature persimmons,and then explored the processing conditions of fermenting black persimmons and the mechanism of fermentation browning of persimmons.1.The effects of four fungi Aspergillus niger,Mucor sp.,Rhizopus sp.,Aspergillus oryzae on persimmon fermentation browning were studied.After a series of treatments,the persimmons were inoculated with four fungi and fermented at 32°C for 72 days.Compared the Browning Degree(BD)of the treatments of these four fungi,Asp.niger was of the greatest effect on fermentation browning.Both the single-factor method and the response surface analysis were used to optimize the persimmon fermentation browning conditions of Asp.niger.The optimal conditions for fermentation were as follows:Asp.niger suspension was 8 m L(1×10-4g/m L),temperature was 33.5°C,and time was 72.5 d,the browning degree(BD)could reach 5.62.2.The persimmons were treated with 8 m L of Asp.niger suspension,the temperature was 33.5°C,and the time was 72.5 d.The relationship between the main nutrients and the browning degree in the fermentation process were studied.The results showed that the BD increased with the prolongation of fermentation time.The crude protein content remained stably at 0.7±0.08%.The free amino acid content changed greatly,with firstly increasing from 0.027 g/kg to 0.043 g/kg and then decreasing to 0.032±0.003 g/kg.The reducing sugar content decreased from 29.74%to 3.82%.The total sugar content decreased from 35.27%to 6.07%.The total acid content decreased from 5.87%to0.073%.The crude fiber content decreased from 6.35%to 4.27±0.02%,and finally remained stably.The ash content remained constantly at 1.34±0.05%.During the fermentation browning of persimmon,the content of main nutrients changed.It may be that the enzyme produced by Asp.niger hydrolyzed the macromolecular substances such as protein,polysaccharide and cellulose in persimmon to produce reducing sugar,free amino acid and others which maybe interacted to form a brown or black substances.3.The browning mechanism of fermented persimmons was studied by the inhibition assay of Melanin synthetic pathway.The results showed that the 3,4-dihydroxyphenylalanine(DOPA),Melanin synthesis pathway inhibitor,was added,the amount of Melanin increased from 0.037 to 0.305,and the amount of Melanin in the control group increased from 0.152 to 0.478.The amount of Melanin of the group added with the inhibitor was 50.1%?310.8%,less than that of the control group.The inhibitory effect was obvious.The amount of synthetic Melanin between the test group added the 1,8-dihydroxynaphthalene(DHN)and the control group was only0.002?0.005,which was not obvious.The result indicated that the pathway of synthesized Melanin of Asp.niger was not the pathway of DHN,but the DOPA Melanin synthesis pathway,to make persimmons brown.4.The browning mechanism of persimmon fermentation was studied by the method of measuring the activity of polyphenol oxidase(PPO)and peroxidase(POD).The results showed that the activities of PPO and POD increased from 29 U/g·min to 50U/g·min and from 15.7 U/g·min to 47.67 U/g·min,respectively,in 10?30 days.And at the 40th day,the activities of PPO and POD were significantly decreased to 0.38U/g·min and 4.76 U/g·min,respectively.The obvious changes of the activities of PPO and POD indicated that persimmon browning was accompanied by enzymatic browning in the fermentation process.Enzymes that produced by Asp.niger during fermentation or that were not completely inactivated in persimmon pulp after autoclaved sterilization interacted with other persimmon components to produce Melanin,to promote the browning of persimmon.5.The browning mechanism of persimmon fermentation was also researched by measuring the content of 5-hydroxymethylfural(5-HMF).The result showed that the content of 5-HMF increased from 1.35 mg/100 g to 4.02 mg/100 g in 10 d?40 d,and decreased from 4.02 to 2.4±0.03 mg/100g in 40 d?50 d,then remained stable,indicating that Melanin was produced along with non-enzymatic browning during peroxidative browning of persimmon,which promoted the browning of persimmon.According to the results of all experiments,browning of persimmon fermentation was a complex browning process,which was the result of the combination of enzymatic browning,non-enzymatic browning,fungal synthesis of Melanin and other reactions with small molecules. |
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